1. Field of the Invention
This invention relates to hardfacing of metal parts and, in particular, to a homogeneous, ductile material useful in hardfacing applications.
Hardfacing is a method of depositing a wear and corrosion resistant layer by melting suitable alloys in-situ. Only one surface of the base metal being hardfaced is brought to the melting point and the hardfacing rod, wire, or powder is melted and spread over the surface of the base metal.
Hardfacing is a fast, economical process used to repair or rebuild worn parts, thereby reducing the overall cost of operation and downtime. The process can be used to build composite parts, combining hardness, toughness and corrosion resistance at low cost. Suitable wear and corrosion resistant surface layers can be imparted to parts e.g. dies and forming tools, which are made of cheaper, shock resistant alloys such as plain carbon or low alloy steels. Moreover, hardfacing is employed in structures wherein a soft core is used to overcome stresses and a hard casing is used to resist wear. Examples of such structures include injection and extrusion screws utilized in plastics processing and the like. Many parts, which would otherwise be scrapped, are put back into service for less than the original cost. An additional saving is realized because the parts can be rebuilt in-situ where necessary.
Conventional hardfacing processes include: oxy-acetylene, tungsten inert gas welding (TIG), metal inert gas welding (MIG), submerged arc weld deposition plasma transferred arc welding and the like. Hardfacing alloys used in such processes contain a substantial amount (about 1 to 11 weight percent) of metalloid elements such as boron, silicon or carbon. Consequently, such alloys are very brittle and are available only in rod form or as powder.
One of the most troublesome problems with conventional hardfacing methods and materials is the difficulty of controlling the thickness and uniformity of the surface layer. The rigid rod-like structures used to advance hardfacing material to the heating zone cannot be economically adapted to continuous surfacing processes. Hardfacing rods are usually applied manually by tungsten inert gas or oxy-acetylene processes which are non-continuous and inherently slow. Continuous hardfacing has been achieved by automatic tungsten inert gas machines in which individual rods are fed by gravity, or by plasma transferred arc (PTA) welding procedures wherein powdered surfacing material is fed to the heating zone. Such procedures require equipment and materials that are relatively expensive. Moreover, the excessive heat generated by the plasma in PTA welding processes adversely affects flowability characteristics of the hardfacing alloy and dilutes the alloy with material from the base metal, changing the compositional uniformity of the surface layer. As a result, there remains a need in the art for an economical, continuous hardfacing process.
Ductile glassy metal alloys have been disclosed in U.S. Pat. No. 3,856,513, issued Dec. 24, 1974 to H. S. Chen et al. These alloys include compositions having the formula M.sub.a Y.sub.b Z.sub.c, where M is a metal selected from the group consisting of iron, nickel, cobalt, vanadium and chromium, Y is an element selected from the group consisting of phosphorus, boron and carbon, and Z is an element selected from the group consisting of aluminum, silicon, tin, germanium, indium, antimony and beryllium, "a" ranges from about 60 to 90 percent, "b" ranges from about 10 to 30 atom percent and "c" ranges from about 0.1 to 15 atom percent. Also disclosed are glassy wires having the formula T.sub.i X.sub.j, where T is at least one transition metal and X is an element selected from the group consisting of phosphorus, boron, carbon, aluminum, silicon, tin, germanium, indium, beryllium and antimony, "i" ranges from about 70 to 87 atom percent. Such materials are conveniently prepared by rapid quenching from the melt using processing techniques that are now well-known in the art. No hardfacing compositions are disclosed therein, however.
There remains a need in the art for a homogeneous, hardfacing material that is available in thin, ductile filamentary form.